| Year | Value | | 2021 | 5.304 | | 2020 | 5.371 | | 2019 | 5.442 | | 2018 | 5.519 | | 2017 | 5.6 | | 2016 | 5.686 | | 2015 | 5.774 | | 2014 | 5.864 | | 2013 | 5.953 | | 2012 | 6.039 | | 2011 | 6.12 | | 2010 | 6.194 | | 2009 | 6.26 | | 2008 | 6.32 | | 2007 | 6.372 | | 2006 | 6.419 | | 2005 | 6.461 | | 2004 | 6.499 | | 2003 | 6.533 | | 2002 | 6.567 | | 2001 | 6.601 | | 2000 | 6.639 | | 1999 | 6.683 | | 1998 | 6.732 | | 1997 | 6.789 | | 1996 | 6.851 | | 1995 | 6.918 | | 1994 | 6.99 | | 1993 | 7.065 | | 1992 | 7.138 | | 1991 | 7.208 | | 1990 | 7.272 | | 1989 | 7.328 | | 1988 | 7.373 | | 1987 | 7.409 | | 1986 | 7.435 | | 1985 | 7.451 | | 1984 | 7.459 | | 1983 | 7.462 | | 1982 | 7.461 | | 1981 | 7.459 | | 1980 | 7.459 | | 1979 | 7.461 | | 1978 | 7.467 | | 1977 | 7.475 | | 1976 | 7.485 | | 1975 | 7.494 | | 1974 | 7.5 | | 1973 | 7.498 | | 1972 | 7.488 | | 1971 | 7.467 | | 1970 | 7.434 | | 1969 | 7.388 | | 1968 | 7.332 | | 1967 | 7.267 | | 1966 | 7.194 | | 1965 | 7.116 | | 1964 | 7.036 | | 1963 | 6.954 | | 1962 | 6.872 | | 1961 | 6.79 | | 1960 | 6.708 |
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